Recently, studies have been under way to form a high-frequency low noise amplifier using an SOI (silicon on insulator) CMOS process (hereinafter, referred to as a SOI process) instead of a SiGe bipolar process (hereinafter, referred to as a SiGe process). The SOI process is generally lower in cost as compared with the SiGe process. In addition, since parasitic capacitance of a MOS transistor formed in the SOI process is usually small, power loss of the high frequency signal is reduced. Accordingly, when the SOI process is used, a high-frequency switch and a high-frequency low noise amplifier may be formed on the same SOI substrate without deterioration of electrical characteristics, whereby a single chip (integrated) product can be realized.
In recent years, there has been a demand for providing a bypass mode for the high-frequency amplifier by which the high-frequency input signal is output without being amplified by the high-frequency low noise amplifier in addition to a gain mode in which the signal is amplified by the high-frequency low noise amplifier.
To configure a circuit in which these two modes can be switched/selected; however, at least three switches are required at the front and back of the high-frequency low noise amplifier. Recently, a multi-band amplifier has been made in which some number of radio signals in different frequency bands can be switched. Accordingly, to make the number of bands switchable and to perform the above-described mode switching for each band, it becomes necessary to provide numerous additional switches. But, in general, it is desirable to reduce the size of the circuit required for mode/band switching as much as possible.